A method for molding glass optical elements, such as high precision lenses, using a mold made from a precisely fabricated mold material, to which softened glass does not adhere and which can be finished to an optical surface, has drawn attentions recently and been developed in a various way. With this method, a simultaneous pressing process for producing plural glass optical elements using plural molds has been researched to improve the productivity of the method. For example, Japanese Unexamined Patent Publication (KOKAI) Showa, No. 63-170,225 discloses a method including the steps of, where four sets of upper and lower cavity dies are arranged in a disc-shaped mold consisted of an upper half and a lower half so that centers of the cavity dies are radially located with the same radius from the center of the mold in being spaced equally from each other, setting a glass material to be molded on each lower cavity die, subjecting the mold to induction heating using induction heating coils wound around mold edges, and heating the cavity dies and the glass material by thermal conductance from the mold to press the glass.
Meanwhile, Japanese Unexamined Patent Publication (KOKAI) Heisei, No. 7-33,452, proposes a molding apparatus for optical elements, as shown in FIG. 12, in which heaters 507 arranged parallel to upper mold halves 502 and lower mold halves 503, which are arranged in series for molding glass materials, heats a shell frame 501 incorporating the upper and lower mold halves 502, 503 to implement a press molding.
To press glass optical elements such as high precision lenses, it is important to make uniform the temperature of the molding surface on the mold, and for instance, such molding needs a temperature profile within 2 or 3.degree. C. The method, disclosed in the above Publication No. 63-170,225, however, creates a temperature profile high at the edge and low at the center of the mold, because the mold edge first receives the induction heating and its heat then conducts in a mold center direction to increase the temperature of the whole mold, and therefore, the molding surface on the cavity die has a temperature profile high at the edge and low at the center of the mold. As a result, the molding material expands on an edge side of the mold, thereby raising a problem that the material comes out of the cavity die. On the center side of the mold, conversely, the material does not so expand, causing possible production of defective articles. Moreover, there raises a problem that the molded articles easily sustain irregularity due to such a temperature profile.
The apparatus disclosed in Japanese Unexamined Patent Publication Heisei, No. 7-33,452 heats the two molds disposed parallel by heating the shell frame using the parallel heaters as shown in FIG. 12. Therefore, the molds are subject to a high temperature on the heater sides and a low temperature on the center of the shell frame, thereby raising the same problem as above. The apparatus of the Patent No. 7-33, 452 not always has a short cycle for molding process, because the molds and glass materials are heated at its heating zone, though the glass material can be automatically supplied and the molded articles are delivered in a sealed chamber.